RingZer0 Team Online CTF (and others) joined

Today we welcome RingZer0 Team Online CTF to WeChall. As the name already suggests, it's a CTF-style site from the RingZer0 Team. It currently has 230 challenges in 13 categories, so there is plenty of work ahead for you!

Also a belated welcome to Challengeland and pwnable.kr that were added in the last "few" months.